The present invention relates to a vehicle-to-vehicle distance detecting apparatus for measuring the distance from a vehicle to a preceding vehicle.
Some typical examples of such a vehicle-to-vehicle distance detecting apparatus are disclosed in Japanese Patent Publication Nos. 63-38085 and 63-46363. The apparatuses disclosed therein commonly have a pair of first and second parallel optical systems having two convex lenses 101, 102 disposed in a horizontally aligned relation at a prescribed distance L away from each other, as shown in FIG. 5. A pair of separate image sensors 103, 104 are horizontally disposed at focuses of the lenses 101, 102 apart their focal distance f from the locations of corresponding lenses 101, 102, respectively, for generating respective image signals to a common signal processor 120. The signal processor 120 successively shifts the image signals from the image sensors 103, 104 and electrically superposes them one over the other, so that the distance R from the lenses 101, 102 to an object 121 is calculated based on the principle of triangulation using the following formula: EQU R=(f.times.L)/d
where d is a shift distance by which the image signals are moved to obtain the best match.
On the other hand, a typical method of tracking a preceding vehicle as taken by an image sensor or the like is disclosed in Japanese Patent Publication No. 60-33352. In this method, for the purpose of tracking a target on a display screen, an operator has to set on the display screen a tracking gate or window which encloses or surrounds the target to be tracked, while looking at the screen.
With the vehicle-to-vehicle distance detecting apparatus as described above which operates to successively detect the distance from a vehicle to a preceding vehicle using, in combination, an optical distance measuring device equipped with an image sensor and a vehicle-image device, it is practically impossible for the driver to safely form a window or tracking gate similar in configuration to the image of the preceding vehicle using a joy stick, a track ball, a mouse and the like, while driving the vehicle, as described in Japanese Patent Publication No. 60-33352.